This invention pertains to amplifiers.
More particularly, the invention pertains to an improved Class D amplifier which does not utilize a clock, which is self-oscillating, and which reduces switching errors and distortions.
Conventional Class D amplifiers are each comprised of an integrator summed with a fixed frequency triangle wave and inputted into the switch control. The switching waveform is filtered through a Low Pass Filter (LPF) and outputted to the speaker or other load. Such amplifiers are illustrated in FIGS. 1 to 3 of U.S. Pat. No. 4,415,863, and have certain disadvantages.
First, the clock frequency in the amplifiers is fixed, resulting in a constant, large, high frequency component that can potentially create noise in FM tuners, switching power supplies, or other parts of an audio system.
Second, the clock frequency is generally selected to optimize operation under heavy load conditions. As a result, when an audio signal input is not applied, poor signal to noise ratio measurements are produced.
Third, the feedback is such prior art systems is taken prior to the low pass filter. This makes it difficult to control the speaker because a nonlinear generation of the sine wave is produced as the load of the speaker changes impedance. This causes poor total harmonic distortion and poor noise and damping factor measurements.
Accordingly, it would be highly desirable to provide an improved Class D amplifier which would compensate for problems caused by a fixed clock frequency and which would yield better speaker control.
Therefore, it is a principal object of the invention to provide an improved Class D amplifier.
A further object of the instant invention is to provide an improved Class D amplifier which reduces the likelihood that excess noise will be created in remaining portions of an audio system used in combination with the Class D amplifier.
Another object of the invention is to provide an improved Class D amplifier which enables better control of a speaker receiving an analog signal from the amplifier.